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The process of surface structuring of a silicon target with femtosecond laser pulses (pulse width ≈180 fs; wavelength λ≈1030 nm) at repetition rates varying from 0.01 to 200 kHz is investigated in vacuum and in air, in static irradiation conditions. The threshold fluence for the formation of a shallow crater, as well as the surface features generated inside the crater, are analyzed at different repetition rate for a fixed sequence of N laser pulses. Our experimental results evidence a clear difference in the morphology of the surface structures generated in vacuum and air, addressing a change in the laser-target energy coupling at the higher pulse repetition rates. The observed behavior is rationalized in terms of the effects induced by the presence of nanoparticle debris, as well as of a plume shielding occurring at repetition rates larger than 10 kHz in air. Both such effects are hindered for vacuum irradiation conditions. Our experimental findings highlight the impact of plume shielding, and nanoparticles coverage on laser material processing in air at high repetition rates. These observations, thus, provide new useful insights in the field of fast laser processing essentially required in many applications of nanoscience and nanotechnologies.

We analyze surface texturing induced by femtosecond laser irradiation of a silicon target at high repetition rates. The features of the produced surface structures in ablative conditions, i.e. at fluences larger than the ablation threshold, are investigated as a function of number of pulses and pulse energy, for various repetition rates, in the range 10 Hz–200 kHz. Our experimental findings highlight a significant influence of the pulse repetition rate on both surface texture and crater size produced by irradiation with a fixed sequence of N laser pulses. This effect is ascribed to plume shielding occurring at repetition rates larger than ≈10 kHz.

The electron-cloud phenomenon is one cause of beam instabilities in high intensity positive particle accelerators. Among the proposed techniques to mitigate or control this detrimental effect, micro-/nano-geometrical modifications of vacuum chamber surfaces are promising to reduce the number of emitted secondary electrons. Femtosecond laser surface structuring readily allows the fabrication of Laser Induced Periodic Surface Structures (LIPSS) and is utilized in several fields, but has not yet been tested for secondary electron emission reduction. In this study, such treatment is carried out on copper samples using linearly and circularly polarized femtosecond laser pulses. The influence of the formed surface textures on the secondary electron yield (SEY) is studied. We investigate the morphological properties as well as the chemical composition by means of SEM, AFM, Raman and XPS analyses. Surface modification with linearly polarized light is more effective than using circularly polarized light, leading to a significant SEY reduction. Even though the SEY maximum is only reduced to a value of ~1.7 compared to standard laser-induced surface roughening approaches, the femtosecond-LIPSS process enables to limit material ablation as well as the production of undesired dust, and drastically reduces the number of redeposited nanoparticles at the surface, which are detrimental for applications in particle accelerators. Moreover, conditioning tests reveal that LIPSS processed Cu can reach SEY values below unity at electron irradiation doses above 10−3 C/mm2.

Liquid processing of 2D crystals offers scalable strategies for the production of 2D materials. Herein, we produce the hybrids of MoS2/graphene, consisting of few-layered nanosheets of luminescent MoS2 and biofunctionalized few-layered graphene assisted by the Vmh2 hydrophobin, a self-assembling adhesive fungal protein, through a green route of production. The functionalization of the graphene flakes assisted by Vmh2 adds surface charge, which enables electrostatic interaction between MoS2 and graphene flakes, leading to the van der Waals coupling. The surface morphology of 2D material based films is analyzed through optical imaging, scanning and transmission electron microscopy. The produced dispersions of MoS2, bGr and the hybrid solutions, are investigated by electrophoretic mobility, UV-Vis, Raman and photoluminescence spectroscopy. Interestingly, the effect of van der Waals interactions between the layers of MoS2 and bGr crystals are evidenced through the significant upshift of 14 cm-1 in the G0 Raman peak of graphene and an upshift of 1.4 cm-1 of the A1g peak of MoS2. Due to the formation of heterostructures, significant quenching of the characteristic photoluminescence emitted from the monolayers of MoS2 was also observed, indicating the charge transfer process occurring between the crystal layers. This approach of scalable synthesis of 2D material based nano-bio hybrids offers economic and eco-friendly solutions to promote novel applications in biosensing and photodetection.

By relying on the photonic immobilization technique of antibodies onto surfaces, we realized portable biosensors for light molecules based on the use of quartz crystal microbalances, given the linear dependence of the method on the laser pulse intensity. Here, we compare the quality of the anchoring method when using nanosecond (260 nm, 25 mJ/pulse, 5 ns, 10 Hz rep. rate) and femtosecond (258 nm, 25 μJ/pulse, 150 fs, 10 kHz rep. rate) laser source, delivering the same energy to the sample with the same average power. As a reference, we also tethered untreated antibodies by means of the passive adsorption. The results are striking: When the antibodies are irradiated with the femtosecond pulses, the deposition on the gold plate is much more ordered than in the other two cases. The effects of UV pulses irradiation onto the antibodies are also analyzed by measuring absorption and fluorescence and suggest the occurrence of remarkable degradation when nanosecond pulses are used likely induced by a larger thermal coupling. In view of the high average power required to activate the antibodies for the achievement of the photonic immobilization technique, we conclude that femtosecond rather than nanosecond laser pulses have to be used.